I really don't think that I am going to be able to keep any more than a 5gal. tank, but what else will I need besides the basics. I want to keep a veiltail and a halfmoon female together. Do you think that this will work? How can I build a divider in case they fight?

Female Bettas are best in groups og 5+ and in 10g+. If you only have a 5g tank and cannot upgrade/get more females... it's best to just divide the tank into two from the beginning :) That way, there is no fatalities :)